1. Field of the Invention
The present invention relates to fluid pressure actuators for rotating a shaft back and forth such as rotating a valve shaft between an open and closed position.
2. Description of the Background
Fluid pressure actuators are old and well known in the art of rotating a shaft such as a valve shaft. These fluid pressure actuators comprise a cylinder in which is located a piston or pistons which are moved back and forth within the cylinder by means of fluid pressure which may be either pneumatic or hydraulic. The piston(s) has a rack associated therewith which engages a pinion attached to the shaft to be rotated and the translation of the piston(s) in the cylinder causes the rack to translate and the pinion to rotate.
In such fluid actuators, it is desirable to provide means for adjusting the stroke of the piston(s) to thereby adjust the rotation of the shaft. This is conventionally accomplished by means of adjusting screws through the end walls of the cylinder, with these adjusting screws engaging piston(s) at the end of the stroke. (See, for example, U.S. Pat. No. 4,566,670.) The problem with such adjusting screws is that they create concentrated loads and localized stresses. This requires the use of high strength materials and/or thick cross sections for the cylinder end caps.